Lactam polymerization with substituted biuret initiators

ABSTRACT

A substituted biuret compound is used as an initiator or activator with alkaline catalyst in the anionic polymerization of lactam monomer so as to provide for a rapid polymerization process.

United States Patent Johnson June 20, 1972 [54] LACTAM POLYMERIZATIONWITH SUBSTITUTED BIURET INITIATORS [72] Inventor: Herbert E. Johnson,South Charleston, W.

Union Carbide Corporation, New York, NY.

[22] Filed: July 9,1970

[21] Appl.No.: 53,667

[73] Assignee:

[52]' U.S. Cl ..260/78 L, 260/78 P [51] Int. Cl. ..C08g 20/12, C08320/18 [58] Field oi'Search ..260/78 L, 78 P [56] References Cited UNITEDSTATES PATENTS 3,028,369 4 1962 Butie retal "266/781,-

3,086,962 4/1963 Mottus et a1. ..260/78 L 3,148,174 9/1964 Glickman et..260/78 P 3,562,221 2/1971 Steinhofer et a]. ..260/78 L [57] ABSTRACT Asubstituted biuret compound is used as an initiator or activator withalkaline catalyst in the anionic polymerization of lactam monomer so asto provide for a rapid polymerization process.

LACTAM POLYMERIZATION WITH SUBSTITUTED BIURET INITIATORS BACKGROUND OFTHE INVENTION 1. Field of the Invention The invention relates to theanionic polymerization of lactam monomer.

2. Description of the Prior Art In the anionic polymerization of lactamsthere is usually employed a catalyst/initiator system. The catalyst iscommonly a material which will form an alkali or alkaline earth metalsalt of the lactam.

Although there are a number of materials known to those in the art asinitiators for such reactions, many of such initiators are notcommercially useful because they either do not provide polymerizationrates which are fast enough in the various types of molding equipmentand processes which are used commercially, and which require relativelyfast processing conditions, or the products produced with suchinitiators do not have commercially acceptable physical properties.

SUMMARY OF THE INVENTION Lactams are anionically polymerized utilizing acatalyst-initiator system whereby the lactam may be readily polymerizedin a relatively short period of time to produce commercially DESCRIPTIONOF THE PREFERRED EMBODIMENT It has now been found that lactams may bepolymerized anionically so as to provide the objects of the presentinvention if there is employed as the catalyst/initiator system for suchpolymerization an anionic catalyst and, as an initiator or activator,one or more substituted biuret compounds.

THE LACTAMS The lactams which may be polymerized according to thepresent invention are all those which are capable of being polymerizedanionically and are preferably those lactam monomers which contain atleast one ring group of the structure H O J. J

wherein n is a whole number which is 3 to 13, and preferably 3 to 10,and R and R' may be the same or different radicals on each carbon atomand may be H or C, to C hydrocarbons.

Such lactams would include those having a single ring structure such asZ-pyrrolidone, 2-piperidone, 6-methyl-2- piperidonc, e-caprolactam,enantholactam, capryllactam, lauryllactam, decanolactam,undecanolacta'rn, dodecanolactam, pentadecanolactam, hexadecanolactam.alkyl substituted caprolactarns, aryl substituted lactams, and the like.

Lactams having a plurality of ring structures which may be used in thepresent invention include bis-lactams such as alkylene bis lactams ofthe formula:

1 13i and 1 m rhe iiiiiis'id polymerized 82in b81558 individually or inany combination thereof.

THE INITIATORS The initiator which is to be employed in the process ofthe present invention is a compound having the structure wherein R R andR may be the same or different radicals which may be C, to C andpreferably C to C saturated or unsaturated hydrocarbon radicals and Rand K, may be the same or different radicals, and may be H or the sameas R,, R and R The hydrocarbon radicals may be aliphatic (linear,branched or cyclic), or aromatic (aryl, aralkyl or alkaryl) in nature.The preferred hydrocarbon radicals are aliphatic radicals, such asmethyl, ethyl, propyl, isopropyl, n-butyl, t-butyl, n-pentyl, n-decyl,2methyl-hexyl-1 and dodecyl; and phenyl.

The hydrocarbon radicals may also be substituted with substituents whichare inert to the other components of the anionic polymerization systemsof the present invention, and to the components of the reaction systemsin which such (I) compounds are prepared.

The initiator compounds may be generally characterized as substitutedbiurets.

These biuret compounds may be prepared in a variety of manners asdisclosed by F. Kurzer in Chemical Reviews, 56, (1956).

One convenient method of preparing the biuret compounds is by thereaction of an allophanoyl halide compound of the structure 1 wherein Xis a halogen radical, i.e. Cl, Br, F, or I, with an amine III of theformula to produce biuret compound I and HX.

Such latter reaction may be conducted at temperatures of about 0 to C.,at atmospheric pressure. The reaction can be conducted in an acidaccepting solvent such as pyridine.

Some of the biuret compounds may be prepared by reacting a suitablysubstituted urea with an isocyanate compound as illustrated by thefollowing reaction:

or compound I where R, H. Examples of these substituted biuret compoundsare l,3,5- trimethyl biuret, i.e., CH NH-CONCH -CO-NHCH l- NcH,co-NH-i-c,rn cii f NH The initiators of the present invention may beused in- R1 MBLWWM dividually or in combination with one another or withone or 0 more other initiators. About 0.1 to moles of initiator are R1 0employed per lOO moles of lactam monomer being 5 \(CHm g polymerized.

10 R2 B: THE POLYMERS 0 The use of the initiators of the presentinvention results in Y I I V the preparation of polymers by thefollowing reactions: X CH2 0 1t, 0 0 /R4 0 I R 0 g N& NJLN\ N ii r NH(CH) 00 N CH) R2 R M+ 011, R/ l 2 6 I IV XI 0 v R1 0 Ba 0 4.! R4

Ji-ir- OH) N M+ 1 5 Thus, depending on the mode of reaction of thecatalyst with R the biuret and the mode of cleavage, the followingstructures VI v for the polymer can be envisioned.

/N -IIT [NH (CHz)5C O] -N-(CH3) R5 R XII \N-J-[NHKJ Ha) s--C O]nN -(CHuh Ra XIII o 0 /JL O 1 O O (C Hz)5-N[( L (CH2) NH n- N -[NH (C H2) s-CO]uN-(C H1);

I la XIV 0 0 Structure XIV arises from the fact that structureVlll andR4 R4 1 Xll still possess a reactive imide group in addition to the lac-1 tam, and, therefore, can function as an initiator also. Thus, the )M+HN (CHM NH M+N CH1) polymer can be any one or a mixture of thesedepending on t V VII a IV the nature of the hydrocarbon residues.

7 The foregoing mechanism was shown for the case when 0 caprolactam ispolymerized. With other lactams, the reaction schemes are similar. Thusa generalized reaction for all laccamlyst tams may be shown by replacingthe moiety (CH in the V CH 2 s I n HN m 7 structures shown above withthe moiety R wherein R would .1. IV represent that portion of thestructure ofthe lactam being polymerized which lies between the nitrogenatom and the carbonyl carbon atom of such lactam. In such reactions,also, H2) R R R R and R, are as defined above, J11 M is the cation ofthe anionic catalyst, and

n is a whole number which is 1 and is such that the III 1 polymersproduced invthe resulting polymeric system are normally solid, i.e.,solid at temperatures of about 25 C. and have reduced viscosities inm-cresol (0.1 gram/100 Other possible inodes of reactions are:

' O ml) at 25 C. of 2 0.4, and preferably about 0.8 to 7, 1\ (I) 0 Rdeciliters/gram.

N--JJ- N -N/ I (3H,)l5 I The value of n may vary somewhat in eachpolymerized lac- R R R ,tam chain, and'wlll be about 10 to about 5,000.The polymers 2 a 4 would thus have molecular weights of about 1,000 to500.000

1 7 IV or more.

, 0 The lactam polymers prepared with the biuret initiators of R1\ 0 0 8the present invention have good physical properties.

i e /NJ $N-- on. THE CATALYST R2 R1 R5 The catalysts which may beemployed in the anionic X polymerization reaction of the presentinvention include all anionic catalyst materials which may be employedin the anionic polymerization of lactams. The catalyst material isusually a salt of the lactam being polymerized although any other lactammay be used to form the catalyst. The salt is usually prepared byreacting the lactam with a strong base, i.e., a base strong enough toconvert the lactam to its salt. Such bases would include alkali andalkaline earth metals or basic derivatives of such metals such as thehydroxides, oxides, alkoxides, phenoxides, hydrides, alkyls, aryls,amides, borohydrides and weak acid salts, i.e., acetates, carbonates,bicarbonates, benzoates, sulfites and bisulfites; Grignard re agents,and various other organometallic compounds. Such bases would include,therefore, metals such as lithium, sodium, potassium, magnesium,calcium, strontium, barium, and aluminum and derivatives of such metals,such as lithium hydroxide, sodium hydroxide, potassium hydroxide,magnesium hydroxide, calcium hydroxide, strontium hydroxide, bariumhydroxide, lithium hydride, sodium hydride, sodium oxide, sodiummethoxide, sodium phenoxide, sodium methyl, sodium ethyl, sodium phenyl,sodium maphthyl, and sodamide; Grignard reagents such as ethyl magnesiumchloride, methyl magnesium bromide, and phenyl magnesium bromide; andother compounds such aszinc diethyl, triisopropyl aluminum, diisobutylaluminum hydride, and lithium aluminum hydride.

About 0.2 to 20,'preferably 0.5 to 6 mole percent of catalyst is usedper mole of monomer being polymerized.

The catalyst and initiator are employed in a mole ratio to each other ofabout 2 to 20, and preferably, 3 to 12.

When the strong base is reacted with the lactam to form the catalyst aby-product is usually formed. For example, hydrogen is formed as aby-product when the metal hydrides or the elemental metals are used;water is formed as a byproduct when metal hydroxides are used; alcoholsare formed when alkoxides are used and water and C0, are formed whencarbonate or bicarbonate salts are used. The preferred catalysts arethose which result in the most readily removable by-products, since someof the by-products, such as H O, may have a deleterious effect on thepolymerization reaction.

THE POLYMERIZATION PROCESS The polymerization reaction is preferablyconducted in bulk. Under such bulk polymerization procedures themonomer, catalyst and initiator are charged in the desired proportionsto the reactor. The bulk polymerization reaction is usually conducted atatmospheric pressure and at a temperature of about 100 to 250 C. Thereaction can be conducted at a temperature which is above or below themelting point of the resulting polymer, and above that of the monomer.The use of elevated pressure is not required for the polymerizationreaction. The bulk polymerization reaction requires a polymerizationperiodof about 3 to l5 minutes at 100-250 C., depending on the lactam(s)employed, and the polymerization temperature. The bulk polymerizationreaction should be carried out under anhydrous conditions, i.e., in thepresence of no more than about 0.3 weight percent, and

preferably no more than 0.03 weight percent, of water or other activehydrogen containing by-product. Where a catalyst is used which wouldgenerate water or other active hydrogen containing by-products, such asthe hydroxide, alkoxide or phenoxide catalysts, the excess amounts ofsuch byproduct materials should be removed before the polymerizationreaction is conducted.

The polymerization is preferably carried out under an inert blanketofgas, such as, nitrogen, argon or helium in order to prevent oxidativedegradation of the monomer and destruction of the catalyst by moisture.

The reaction may be carried out batchwise or continuously. Anadvantageous method of carrying out the reaction of the presentinvention is to conduct the bulk polymerization in conventional moldingequipment such as a rotational casting device or a compression moldingmachine, or an extruder. In this way the polymer and the molded objectscan both be formed in one step. Where the polymerization is conducted insuch molding devices, conventional molding pressures may be employed inorder to simultaneously form the molded object with the in situ formedpolymer.

Since the lactams are normally solid materials at room temperatures, thebulk polymerization reactions may be carried out by various procedures.In one procedure, the lactam may be melted, and both the catalyst andthe initiator admixed with it and then the reaction may be caused toproceed by bringing the reaction mixture to polymerization temperatures.

' In another procedure, the catalyst and initiator may be dissolvedseparately in the lactam monomer, after which the two separate solutionsmay be combined to cause the polymerization to proceed at polymerizationtemperatures. Where the polymerization is conducted in moldingequipment, the equipment may be heated to the desired polymerizationtemperature in order to effect polymerization upon injection therein ofthe polymerization reaction system.

In addition to being conducted in bulk, the polymerization may also beconducted in high boiling inert organic solvents, i.e., those havingboiling points of about C., such as chlorobenzene, dichlorobenzene,xylene, trichlorobenzene dimethyl sulfoxide, N-alkyl pyrrolidones andhexamethylphosphoramide at temperatures of about 100 C. up to theboiling point of the solvent; or at temperatures of about to 240 C. indispersion systems such as those disclosed in US. Pat. Nos. 3,061,592and 3,383,352, and by 0.8. Gechele and G.F. Martins in J. AppliedPolymer Science 9, 2939 ADJUVANTS The polymerization reaction of thepresent invention may also be conducted in the presence of various typesof adjuvant materials which are normally employed with the types ofpolymers prepared by the present invention, or the adjuvants may beadded to the polymer after it is formed. Such adjuvant materials wouldinclude fillers, stabilizers, fibrous reinforcing agents such asasbestos and glass fiber, and pigmenting materials.

The particular polymer being prepared as well as the end use applicationwill dictate the selection and quantity of the adjuvant to be employedtherewith since it is the respective adjuvants for such polymers andsuch applications that are to be employed in the present invention. Theadjuvants employed must be physically and chemically compatible witheach of the other components of the monomer and polymer basedcompositions, under the prescribed operating conditions. As such, wherethey are present during the polymerization reaction, the adjuvantsshould not contain reactive groups which would interfere with thepolymerization reactions, such as active hydrogen containing groups suchas carboxyl, amino, mercaptan or hydroxyl groups.

The adjuvants would be used in amounts which would be effective forintended purpose. Thus, a stabilizer would be used in a stabilizinglyeffective quantity, and the fillers would be used in effectivequantities therefor. For example, if a reinforcing filler were to beused, such filler should be used in such amounts as to provide thedesired reinforcing effect.

The polymers made by the process of the present invention may be usedfor a number of applications which require the use of molded articlesprepared from lactam polymers such as fibers, films, engineeringstructures, coatings and hollow articles such as tubing and solventtanks.

The following examples are merely illustrative of the present inventionand are not intended as a limitation upon the scope thereof.

The general procedure employed for the polymerization of e-caprolactamin the examples herein is as follows:

into each of two 25 X 200 mm test tubes was added 28.3 g.

(0.25 mole) of dry 2. 0.03 percent H O) molten e-caprolactam, and bothwere then heated at the desired polymeration temperature. Sodium hydridein the form of a dispersion (57 percent) in mineral oil was added to oneof these test tubes, while the initiator was added to the other. Aftersolutions were formed and equilibrated with the bath temperature, theywere mixed and a thermocouple was inserted in the resulting mix-v ture.The progress of the polymerization was followed both visually and byobserving the reaction temperature which, due to the exotherm of thereaction, rises initially. Thus the rate with which the reaction reachespeak temperature is an indication of the polymerization rate. The timerequired for the development of opacity was taken as an indication ofthe time required for crystallization of the Nylon 6 formed.

EXAMPLE 1 EXAMPLE 2 A lower molecular weight Nylon 6 product wasprepared by using 0.9 mole percent of l,3,5-trimethylbiuret as theinitiator with 2 mole percent of NaH catalyst at 140 C. Under theseconditions, the crystallization time was 40 seconds, and after a minuteheating cycle that R.V. (reduced viscosity) of the polymer'was 0.78 andthe percent of water insoluble values in the polymer was 97.5.

EXAMPLE 3 Very high molecular weight polymer can be prepared byconducting the polymerization with low concentrations of initiator andcatalyst. Thus, when 0.3 mole percent of l,3,5- trimethylbiuret was usedwith 0.5 mole percent catalyst, the crystallization time was 2.5minutes, and after 5 minutes heating cycle at 155 C. the RV. was foundto be 2.12.

The color of the polymers produced in the examples was a good, oiY-whitecolor. 7

and 7, had a good off-white color. The initiators used in Examples 4 and5, i.e., biuret, Nl-i CO-NH-CONH and 1,3- dimethyl biuret, Cl-iNl-iCO-NCH,-CONH,, did not produce any polymer as noted. These examplesthus illustrate the utility of the specific substituted biuret compoundsof the present invention as lactam anionic polymerization initiators.

The speed with which the tested biuret compounds functioned asinitiators is disclosed below in Table II, which lists the initiatorused, and, where applicable, the resulting no flow time andcrystallization time achieved with each of the initiators.

TABLE II Crystal- No flow llzation time, time,

Example Initiator minutes minutes 4. Biuret 5- 1,3-dimethyl biure 6.1,3-dimethyl-5-(2-methoxyethyl)- 1 1.5

biuret. 7 1-n-butyl3-meth l-fi-(m-trifluoro- 3.5 4

methyl-phenyl biuret.

i No polymerization observed after 1 hour. 2 N o polymerization observedalter /5 hour.

What is claimed is: 1

l. A process for anionically polymerizing e-caprolactam to a moldablepolymer with an anionic lactam polymerization catalyst and an anioniclactam polymerization initiator which comprises using as said initiatorat least one biuret compound having the structure R1\ 0 Illa 0 /R4N-PJ-N--N wherein R,, R and R are the same or different monovalentradicals and are C to C hydrocarbon radicals which are unsubstituted orsubstituted with substituents which are inert to the other components ofthe polymerization system, and

R and R are the same or different monovalent radicals and are H or C, toC hydrocarbon radicals which are unsubstituted or substituted withsubstituents which are inert to the other components of thepolymerization system.

2. A process as in claim 1 in which R and R are H.

3. A process as in claim 2 in which said biuret compound is TABLEI.-COMPARISON 0F INITIATOR EFFICIENCY Time for Polymor- Time forcrystal- Heat cycle Percent izntion no flow lization time :1 H20 Ex-R.V., initiator temp., 0. seconds seconds 150 C. tractable dl./gm

1,3,5-trimethyl biuret 150 5 2. 8 1. 12 Diphenylurea 160 390 600 12 21.8 'IDI 150 24 32 5 3. 7 gel 24 hours boiling H20 Soxlet extraction.

b 0.1 gin/100 ml. m-cresol a heat cycle time.)

EXAMPLES 4-7 Using the procedure noted above, various biuret compoundswere tested as e-caprolactam polymerization initiators. Thepolymerization reactions were conducted at 150 C. using 2 mole percentof Nal-i as catalyst and 0.5 mole percent of the biuret compound. asinitiator. The polymers produced with the initiatorsof the presentinvention, i.e. in Examples 6 t 25 C. (a and b are tests conducted onthe polymeric products produced after full 0-1050 7. U DSTATES'ISPATFENT OFFECE.

CERTIFICATE 01 'CORRECTIDN Patent No. 3,671,?"Sdl I i Y Dat d I June "20, lnventbfls) Herbert 2E Johnson v I It is certified that error appearsin the above-identified patent and that said Letters Patent .are herebycorrected as shown below:

Column 1, lines 71-75, that portion of the formula reading C=0 shouldread (cR R r (cR R --NH C=O (CR R II Column 2 line 42 "56" should read 6Column 4, line 32, that portion of structure XII reading -N- should readN R R3 Column 5, line 21, "maphthyl" should read --naphthyl--;

Column 7 line 1, "A" should read Signed and sealed this" 2nd day" ofJanuary 1973 SEAL l ttes cz EDWARD M .,FLETCHER,JR 7 ROBERT GOTTSCHALKAttesting Officer Commissioner of Patents

2. A process as in claim 1 in which R2 and R4 are H.
 3. A process as in claim 2 in which said biuret compound is 1,3, 5-trimethyl biuret.
 4. A process as in claim 2 in which said biuret compound is 1,3-dimethyl-5-(2''-methoxyethyl)biuret.
 5. A process as in claim 2 in which said biuret compound is 1-n-butyl-3-methyl-5-(m-trifluoromethylphenyl)-biuret.
 6. A process as in claim 1 which is conducted in a shaping device with the simultaneous formation of a shaped object. 